High resolution UV spectroscopy of H-2 and N-2 applied to observations of the planets by spacecraft

The next generation of high resolution UV imaging spacecraft are being prepared for studying the airglow and aurora of the Earth, the other terrestrial planets and the Jovian planets. To keep pace with these technological improvements we have developed a laboratory program to provide electron impact collision cross sections of the major molecular planetary gases (H-2 N-2, CO2, O-2 and CO). Spectra under optically thin conditions have been measured with a high resolution (lambda/Delta lambda = 50000) UV spectrometer in tandem with electron impact collision chamber. High resolution spectra of the Lyman and Werner band systems of H-2 have been obtained and modeled. Synthetic spectral intensities based on the J-dependent transition probabilities that include ro-vibronic perturbations ate in very good agreement with experimental intensities. The kinetic energy distribution of H(2p,3p) atoms resulting from electron impact dissociation of H-2 has been measured. The distribution is based on the first measurement of the H Lyman-alpha (H L alpha) and H Lyman-beta (H L beta) emission line Doppler profiles. Electron impact dissociation of H-2 is believed to be one of the major mechanisms leading to the observed wide profile of H L alpha from Jupiter aurora by the Hubble Space Telescope (HST). Analysis of the deconvolved line profile of H L alpha reveals the existence of a narrow line peak (40 m Angstrom FWHM) and a broad pedestal base (240 m Angstrom FWHM). The band strengths of the electron excited N-2(C-3 Pi(u)-B-3 Pi(g)) second positive system have been measured in the middle ultraviolet. We report a quantitative measurement of the predissociation fraction 0.15+/- (.01)(.045) at 300 K in the N(2)c'(1)(4) Sigma(u)(+)-X(1) Sigma(g)(+) (0,0) band, with an experimental determination of rotational line strengths to be used to understand N-2 EUV emission from Titan, Triton and the Earth.